Confused about transformer - will this work?

Never tried back-feeding a transformer from a phase converter. I think I would first check twith the converter Mfg to see if there are any issues since the 3-phase that is created by the converter is not the same as that from the utility. As far as the transformer you could put 208V on the xfmr secondary (do not run a neutral or ground the neutral terminal) and you will get 600V on what is now the primary terminals. You usually cannot back-feed small transformers or control transformers but 15KVA should not be a problem. You will be creating a separately derived system and need to provide a 600V fusible switch and overcurrent protection. You could also be getting into the requirement that one phase of the 600V be grounded (corner grounded delta). Since I assume this is not portable equipment and not premises wiring it may not be required to ground the system but it is allowed.

I believe so Still, but what do you mean by "208Y"

….while I hafta admit I don't know what's a phase converter

Edited to remark that Bah knows a whole lot more about this kind of thing than I

Thanks. This is going to be a permanent site for this lathe as you thought. I'm still confused about the wiring so I'll just explain what I have done and maybe you can spot my problem. There's a green wire coming from the transformer that I assumed was ground so I ran this wire to the shop grounding rod. There was a white wire coming from the same area as the green wire that I did nothing with - just laying on the floor loose. I attached the 3 secondary (red, black and blue) along with a ground to a four prong plug that was compatible with my converter. I plugged it into my phase converter. I direct wired the primaries into the lathe. Nothing happened. Any thoughts? Thanks.

I would check to see that you have 208 3 pH at your converter. Then connect the transformer secondary phase conductors and see if you get 600 volts at the transformer primary before you connect to the lathe. It could be the phase converter cannot be used this way, I don't know for sure. You should contact the phase converter Mfg to see if it can be used this way. Make sure you are looking at the transformer terminals and not guessing what the wires are. Make sure the transformer neutral is not bonded to the transformer case and ground. If you try and back feed with a bonded neutral you will probably blow a fuse or trip a breaker on the 208 volts.